A 50-year-old woman, who presented with progressive androgenization, central obesity and severe hypertension, was initially suspected to have an adrenal virilizing tumor. Her serum testosterone level was in the male range (9.3-11.6 ng/ml) and was not suppressed with dexamethasone. Although no pathological abdominal or pelvic mass was detected, total hysterectomy and bilateral salpingo-oophorectomy was performed. Histopathological examination revealed a theca-cell tumor of the right ovary. Postoperatively the testosterone level returned to normal and the patient had regression of virilism. Our case illustrates that a virilizing ovarian tumor can be small and elude imaging studies, but may be detected by means of well-considered clinical management.